Research in psychology and neurophysiology requires the correlation of stimuli with the responses they elicit. In studies of the sensory and motor systems, this requires that the behavior of the subject be controlled and that the data be collected by a high-speed digital computer. The current state of software development for such laboratory computer systems is limited to three types of programs. The first type includes special purpose programs which are designed to elicit a certain class of behavior from the subject and collect specific quantities as data. The second type includes general purpose behavioral controllers with only nominal data collection provisions. The third type includes general purpose data collection programs with little or no provision for behavioral control. This project has been devoted to creating a fourth class of experimental research programs. Known as the REX (Real-time Experimentation) system, it is actually a collection of program modules which can be combined at the time of the experiment to perform both behavioral control and data collection in either laboratory or clinical applications.